This invention is related to dosimeters, and more particularly, miniature dosimeters which are injectable into the human body.
Radiation therapy is commonly used to destroy tumor cells in humans and animals. The idea is to deliver enough ionizing energy to destroy tumor cells but limit the amount of energy to avoid significant damage to surrounding normal cells and tissue. Radiation delivered to the tissue is calculated by measuring the energy output, the distance from the energy source to the target tissue, and the radiation absorption of the tissue that the radiation has to penetrate. Many assumptions, which are not always accurate, have to be made. Furthermore, the radiation delivered to one area of the target may be different from another area because of different tissue density and distance from the energy source. For example, radiation will penetrate through solid tissue differently from hollow tissue with air or hollow tissue with liquid. Although tumors on the surface of the skin are easy to dose accurately, tumors deep in a body cavity, such as the abdomen, chest, or brain cannot always be dosed precisely. Dosing can be particularly difficult in the pelvis, where several different types of structures exist with different densities, such as the bowel, ureter, blood vessels, and solid organs. Normal tissue is inevitably destroyed, often in a clinically significant manner because of the imprecise nature of the radiation-dosing procedures currently available. The consequences of imprecise radiation include ineffective treatment of tumors in cases of under-radiation, and destroying healthy tissue in cases of over-radiation. Serious complications such has vaginal-rectal fistulas can arise from radiating healthy tissue. In most other areas, tumor and the normal tissue are demarcated by a red marking pen on the skin when possible and the area for the radiation is calculated using physical properties of distance, which is again very imprecise.
Numerous radiation dosimeters have been proposed. For example, U.S. Pat. No. 4,381,450 by Cappelli, entitled xe2x80x9cPulsed Radiation Dosimetry Apparatus,xe2x80x9d issued Apr. 26, 1983, describes a pulsed radiation dosimetry apparatus utilizing a pin diode to detect pulsed radiation. The detected radiation signal is integrated and then displayed directly on a digital meter providing a direct readout of radiation dose in rads. U.S. Pat. No. 4,999,504 by Braunlich et al., entitled xe2x80x9cRemote Radiation Dosimetry,xe2x80x9d issued Mar. 12, 1991, describes a remote radiation dosimetry apparatus using a beam generator, such as a laser beam, to provide a stimulating beam. The stimulating beam is used to stimulate a remote luminescent sensor mounted on a probe, which emits stored luminescent energy resulting from exposure of the sensor to ionizing radiation. The stimulating beam is communicated to the remote luminescent sensor via transmissive fiber which also serves to return the emission from the luminescent sensor. The stimulating beam is further split by a beam splitter to create a detector beam which is measured for power during a reading period during which the luminescent phosphor is read. The detected power is then used to control the beam generator and thus produce the desired beam power. U.S. Pat. No. 5,115,134 by Slowey, entitled xe2x80x9cPrecise Low Energy Radiation Dosimetry,xe2x80x9d issued May 19, 1992, describes a precise low energy radiation dosimetry system using an ionization chamber with a beryllium window. A conductive carbon coating, including lithium and fluorine, provides secondary electron emissions to flatten response of the beryllium window in the desired radiation energy range without the use of external mathematical correction factors.
U.S. Pat. No. 5,637,876 by Donahue et al., entitled xe2x80x9cRadiation Dosimetry Method and Apparatus,xe2x80x9d issued Jun. 10, 1997, describes a radiation dosimetry apparatus comprising a substrate that is radiation sensitive and has optical density which varies in accord with the degree of radiation exposure. The substrate is also provided with an optically readable code, which identifies encoded mathematical parameters to enable an automated calculation dosage from a detected post-exposure optical density of the radiation sensitive material. Each dosimeter is provided with a unique identification code encoded in the bar coding on the dosimeter substrate.
This enables memory storage of pre-exposure optical density as a baseline reference to be used in order to calculate the radiation dose when compared to the postexposure density. U.S. Pat. No. 5,767,520 by Donahue et al., entitled xe2x80x9cRadiation Dosimetry Method and Apparatus,xe2x80x9d issued Jun. 16, 1998, describes a plurality of pre-exposure optical densities and a plurality of post-exposure optical densities of the layer of radiation sensitive material in a plurality of wavelength bands to allow optical measurement of the radiation dose at multiple time periods. U.S. Pat. No. 5,811,822 by Huston et al., entitled xe2x80x9cOptically Transparent, Optically Stimulable Glass Composites For Radiation Dosimetry,xe2x80x9d issued Sep. 22, 1998, describes an optically transparent and optically stimulable glass composite for radiation dosimetry. In this invention, a glass matrix is doped with various radiation sensitive elements. An article entitled xe2x80x9cGeneral Specifications for Silicon Semiconductors for Use in Radiation Dosimetry,xe2x80x9d by Swedish researchers Rikner and Grusell, published in PHYsics MEDICINE BIOLOGY, Vol. 31, No. 9, 1109-1117, (copyright)1987 IOP Publishing Ltd., describes the characteristics of diodes used as radiation detectors.
All of the above references describe a radiation dosimetry system capable of detecting and quantifying the radiation dose. However, all but one of the above references describe a dosimeter that must be directly and physically accessible. This requires the dosimeter to be on the surface of the patient and thus, the previous patents have limited clinical application, particularly in tumors that are seated deep in the chest or abdomen. Although the abovementioned U.S. Pat. No. 4,999,504 allows remote sensing by using laser beams, lasers can only penetrate tissue to a limited depth. Furthermore, none of the above inventions allows precise determination of the location of the sensor in the depths of the body.
All of the previous inventions measure radiation in a one-dimensional surface and do not consider radiation in all directions, including scatter. The dosimeters are large and cannot be placed in many multiple sites.
The present invention disclosed and claimed herein, in one aspect thereof, comprises a system for detecting a dosage of radiation received by a tumor during radiation treatment. A radiation source is directed at the tumor. A central processing unit connects to the radiation source for monitoring and controlling the radiation treatment. One or more dosimetry transponders are injected into the tumor, each the dosimetry transponder having, a communication circuit for communicating power and control signals between the transponder and the central processing unit, and one or more detectors for detecting radiation and converting the detected radiation to a data signal.